The present invention relates to a newly identified human aminopeptidase. The invention also relates to polynucleotides encoding the aminopeptidase. The invention further relates to methods using the aminopeptidase polypeptides and polynucleotides as a target for diagnosis and treatment in aminopeptidase-related disorders. The invention further relates to drug-screening methods using the aminopeptidase polypeptides and polynucleotides to identify agonists and antagonists for diagnosis and treatment. The invention further encompasses agonists and antagonists based on the aminopeptidase polypeptides and polynucleotides. The invention further relates to procedures for producing the aminopeptidase polypeptides and polynucleotides.
Proteases may function in carcinogenesis by inactivating or activating regulators of the cell cycle, differentiation, programmed cell death, or other processes affecting cancer development and/or progression. Consistent with the model involving protease activity and tumor progression, certain protease inhibitors have been shown to be effective inhibitors of carcinogenesis both in vitro and in vivo.
Aminopeptidases
Aminopeptidases (APs) are a group of widely distributed exopeptidases that catalyse the hydrolysis of amino acid residues from the amino-terminus of polypeptides and proteins. The enzymes are found in plant and animal tissue, in eukaryotes and prokaryotes, and in secreted and soluble forms. Biological functions of aminopeptidases include protein maturation, terminal degradation of proteins, hormone level regulation, and cell-cycle control.
The enzymes are implicated in a host of conditions and disorders including aging, cancers, cataracts, cystic fibrosis and leukemias. In eukaryotes, APs are associated with removal of the initiator methionine. In prokaryotes the methionine is removed by methionine aminopeptidase subsequent to removal of the N-formyl group from the initiator N-formyl methionine, facilitating subsequent modifications such as N-acetylation and N-myristoylation. In E. coli AP-A (pepA), the xerB gene product is required for stabilization of unstable plasmid multimers.
APs are also involved in the metabolism of secreted regulatory molecules, such as hormones and neurotransmitters, and modulation of cell-cell interactions. In mammalian cells and tissues, the enzymes are apparently required for terminal stages of protein degradation, and EGF-induced cell-cycle control; and may have a role in protein turnover and selective elimination of obsolete or defective proteins. Furthermore, the enzymes are implicated in the supply of amino acids and energy during starvation and/or differentiation, and degradation of transported exogenous peptides to amino acids for nutrition. As leukotriene A4 hydrolase may be an aminopeptidase, APs may further have a role in inflammation. Industrial uses of the enzymes include modification of amino termini in recombinantly expressed proteins. See A. Taylor (1993) TIBS 18: 1993:167-172.
A variety of aminopeptidases have been identified from a wide variety of tissues and organisms, including zinc aminopeptidase and aminopeptidase M from kidney; arginine aminopeptidase from liver; aminopeptidase Nb from muscle; leucine aminopeptidase (LAP) from lens and kidney; aminopeptidase A (xerB gene product) from E. coli; yscl APE1/LAP4 and aminopeptidase A (pep4 gene product) from S. cerevisiae; LAP from Aeromonas; dipeptidase from mouse ascites; methionine aminopeptidase from Salmonella, E. coli, S. cerevisiae and hog liver; and D-amino acid aminopeptidase from Ochrobactrum anthropi SCRC C1-38.
Of these aminopeptidases, the structure of bovine lens leucine aminopeptidase (blLAP) is well-characterized and consists of a homohexamer synthesized as a large precursor, each monomer containing two thirds of the protein in a major lobe and one third in a minor lobe. The minor lobe contains the N-terminal 150 residues. All putative active site residues, presumably also the inhibitor bestatin-binding site, are found in the C-terminal lobe and include Ala-333, Asn-330, Leu360, Asp332, Asp255, Glu-334, Lys250, Asp273, Met-454, Ala-451, Gly362, Thr-359, Met270, Lys262, Gly362 and Ile-421.
Many aminopeptidases are metalloenzymes, requiring divalent cations, with specificities for Zn2+ or Co2+. However, particular sites of certain aminopeptidases can readily utilize Mn2+ and Mg2+. Residues used to ligand Zn2+ include the His Glu and Asp Glu Lys configurations. In addition to bestatin, boronic and phosphonic acids, xcex1-methylleucine and isoamylthioamide are identified as competitive inhibitors for most aminopeptidases. See A. Taylor (1993) TIBS 18: 1993:167-172; Burley et al. (1992) J. Mol. Biol. 224:113-140; Taylor et al. (1993) Biochemistry 32:784-790.
Aminopeptidases from various organisms and various tissues within an organism have high degrees of primary sequence homology, as indicated by immunological assays. Some enzymes also exhibit very similar kinetic profiles. Direct amino acid sequence comparison of blLAP and aminopeptidase-A from E. coli shows 18, 44 and 35% identity for the amino- and carboxy-terminals, and the entire protein, respectively. The comparison shows 46, 66, and 60% identity for the respective regions. See Burley et al. (1992) J. Mol. Biol. 224:113-140.
Bovine lens leucine aminopeptidase (blLAP), bovine kidney LAP, human lens and liver LAPs, hog lens, kidney and intestine LAPs, proline-AP, E. coli AP-A, AP-I and the S. typhimurium pepA gene product have been categorized as belonging to the family of zinc aminopeptidases which utilize the residues Asp Glu Lys for zinc binding and the active site amino acid configuration described above for bovine LAP for substrate binding. This family, possibly also including Aeromonas LAP, is suggested to be distinguished from zinc proteases which utilize His His Glu in zinc binding and Arg in substrate binding. The Saccharomyces methionine-AP is characterized to contain two zinc finger like motifs in the amino-terminus and shares little homology with blLAP. See A. Taylor (1993) TIBS 18:167-171; Watt et al. (1989) J. Biol. Chem. 264:5480-5487.
Leucine aminopeptidase expression is regulated at the transcriptional level, evidenced by enhancement of both activity and mRNA upon removal of serum in in vitro aged and/or transforming lens epithelial cells. Furthermore, LAP mRNA and protein are induced by interferon y in human ACHN renal carcinoma, A549 lung carcinoma, HS153 fibroblasts and A375 melanoma. Regulation by development and growth is also implicated. The E. coli pepN gene is transcriptionally regulated upon anaerobiosis and phosphate starvation. Membrane bound AP-N (CD 13) is expressed in a lineage-restricted manner by subsets of normal and malignant cells, apparently through regulation by physically distinct promoters. Expression of the yeast yscI product APE1 is dependent upon the levels of yscA and PEP4 gene products. Synthesis of APE1 is sensitive to media glucose levels, and the activity of yeast aminopeptidase is sensitive to substitution of ammonia rather than peptone as the source of nitrogen. See Harris et al. (1992) J. Biol. Chem. 267:6865-6869; Jones et al. (1982) Genetics 102:665-677.
Aminopeptidase B
Aminopeptidase B is an exopeptidase that removes arginine and/or lysine from various amino terminal peptide substrates. This enzyme is structurally related to leukotriene A4 hydrolase. The activity of aminopeptidase B is dependent upon Zn2+. With respect to primary structure, the enzyme isolated from rat testis exhibits an amino terminal potential signal peptide and a Zn2+ binding consensus sequence (HEXXHX18E). In view of the fact that the enzyme contains this consensus sequence, the enzyme can be classified as a M1 family metallopeptidase.
In the M1 family, the aminopeptidase is most closely related to the leukotriene A4 hydrolase. Accordingly, in addition to the aminopeptidase activity, the enzyme contains leukotriene A4 epoxide hydrolase activity. The specific enzyme from rat testis also contains a fully conserved ribonucleoprotein binding site ([RK]-G-[AFILMNQSTVWY]-[AGSCI]-[FY]-[LIVA]-X-[FYM]; SEQ ID NO:3). The enzyme also contains a potential nuclear localisation (KKK; SEQ ID NO:4)) and a consensus (KGYCFVSY; SEQ ID NO:5) ribonucleoprotein binding motif. Based on these features it has been proposed that the enzyme could be transported to the nucleus where it could be interacting with specific nuclear proteins. See Foulon et al. (1999) Int. J. Biochem. Cell Biol. 31:747-750.
Aminopeptidase B exopeptidase activity was originally identified using L-aminoacyl xcex2-naphthylamide and L-amino acid 7-amido-4-methylcoumarins. It was also shown that the enzyme could cleave the lysine residue from the amino terminus of kallidin but could not hydrolyse the arginine-proline of bradykinin. The enzyme purified from rat testis acts on substrates including Arg0-Leu-enkephalin, Arg0-Met-enkephalin and Arg1-Lys6-somatostatin-14.
Foulon et al. characterize aminopeptidase B as specifically removing basic amino acid residues from aminoacyl xcex2-naphthylamides and from the amino terminus of various peptides such as kallidin 10, Met5-enkephalin, [Arg0]-Leu5-enkephalin, [Argxe2x88x921-Lys0]-somatostatin-14, neurokinin, natriuretic factor and thymopentin. Further, the enzyme is characterized as being sensitive to classical inhibitors of aminopeptidases such as bestatin and arphamenine. Further, it is able to hydrolyse leukotriene A4, the natural substrate of leukotriene A4 hydrolase into leukotriene B4, a lipid mediator of inflammation.
Based on the structural and biochemical information, Foulon et al. have proposed that the aminopeptidase B is associated with post-translational maturation in the trans-Golgi network and regulatory processes in the plasma membrane, including extracellular processing of various peptide substrates. It was further proposed that in the acrosome of spermatids, the aminopeptidase could participate in maturation of proenkephalin and procholecystokinin. In the inflammatory process, it is suggested that potential substrates of the aminopeptidase B include kallidins, enkephalins and somatostatin.
Accordingly, aminopeptidases are a major target for drug action and development. Therefore, it is valuable to the field of pharmaceutical development to identify and characterize previously unknown aminopeptidases. The present invention advances the state of the art by providing a previously unidentified human aminopeptidase.
It is an object of the invention to identify novel aminopeptidases.
It is a further object of the invention to provide novel aminopeptidase polypeptides that are useful as reagents or targets in aminopeptidase assays applicable to treatment and diagnosis of aminopeptidase-related disorders.
It is a further object of the invention to provide polynucleotides corresponding to the novel aminopeptidase polypeptides that are useful as targets and reagents in aminopeptidase assays applicable to treatment and diagnosis of aminopeptidase-related disorders and useful for producing novel aminopeptidase polypeptides by recombinant methods.
A specific object of the invention is to identify compounds that act as agonists and antagonists and modulate the expression of the novel aminopeptidase.
A further specific object of the invention is to provide compounds that modulate expression of the aminopeptidase for treatment and diagnosis of aminopeptidase-related disorders.
The invention is thus based on the identification of a novel human aminopeptidase, a human ortholog of rat aminopeptidase B. The amino acid sequence is shown in SEQ ID NO 1. The nucleotide sequence is shown as SEQ ID NO 2.
The invention provides isolated aminopeptidase polypeptides, including a polypeptide having the amino acid sequence shown in SEQ ID NO: 1 or the amino acid sequence encoded by the cDNA deposited as ATCC Patent Deposit No. PTA-2811 on Dec. 15, 2000 (xe2x80x9cthe deposited cDNAxe2x80x9d).
The invention also provides isolated aminopeptidase nucleic acid molecules having the sequence shown in SEQ ID NO 2 or in the deposited cDNA.
The invention also provides variant polypeptides having an amino acid sequence that is substantially homologous to the amino acid sequence shown in SEQ ID NO 1 or encoded by the deposited cDNA.
The invention also provides variant nucleic acid sequences that are substantially homologous to the nucleotide sequence shown in SEQ ID NO 2 or in the deposited CDNA.
The invention also provides fragments of the polypeptide shown in SEQ ID NO 1 and nucleotide sequence shown in SEQ ID NO 2, as well as substantially homologous fragments of the polypeptide or nucleic acid.
The invention further provides nucleic acid constructs comprising the nucleic acid molecules described herein. In a preferred embodiment, the nucleic acid molecules of the invention are operatively linked to a regulatory sequence.
The invention also provides vectors and host cells for expressing the aminopeptidase nucleic acid molecules and polypeptides, and particularly recombinant vectors and host cells.
The invention also provides methods of making the vectors and host cells and methods for using them to produce the aminopeptidase nucleic acid molecules and polypeptides.
The invention also provides antibodies or antigen-binding fragments thereof that selectively bind the aminopeptidase polypeptides and fragments.
The invention also provides methods of screening for compounds that modulate expression or activity of the aminopeptidase polypeptides or nucleic acid (RNA or DNA).
The invention also provides a process for modulating aminopeptidase polypeptide or nucleic acid expression or activity, especially using the screened compounds. Modulation may be used to treat conditions related to aberrant activity or expression of the aminopeptidase polypeptides or nucleic acids.
The invention also provides assays for determining the activity of or the presence or absence of the aminopeptidase polypeptides or nucleic acid molecules in a biological sample, including for disease diagnosis.
The invention also provides assays for determining the presence of a mutation in the polypeptides or nucleic acid molecules, including for disease diagnosis.
In still a further embodiment, the invention provides a computer readable means containing the nucleotide and/or amino acid sequences of the nucleic acids and polypeptides of the invention, respectively.